Possibility of using caustic residue from bauxite for improving the chemical and physical properties of sandy soils

Abstract

Large quantities of alkaline red mud are produced as a waste product from the extraction of alumina from bauxite. Its chemical and physical properties and the way that it could be modified to produce good growth of plants were investigated. The cation exchange capacity of the red mud increased with pH, the adsorption of phosphate decreased, and the adsorption of cadmium increased. A pH of just above eight seemed to provide a good combination of desirable properties. This could be achieved by exposing the red mud to air and mixing it with gypsum - also available as a waste product. Carbon dioxide was absorbed by alkaIi in the red mud, and then precipitated by the gypsum as calcium carbonate. This released sodium sulfate which could be leached from the mud. Medic species could then be grown, provided that phosphate, potassium and manganese were supplied. Residual sodium sulfate from incomplete leaching seemed to limit the growth of other species. There seemed to be a potential to use the amended red mud to improve the waterholding properties and the chemical properties of sandy soils of the Western Australian coastal plain.